Telit Wireless Solutions GM862-GPS Manuel d'utilisateur télécharger pdf (Page 32)

GM862-GPS Hardware User Guide

1vv0300728 Rev. 0 - 27/04/06

NOTE: The cable to the microphone should not be shielded, instead a twisted pair cable shall

be used.

NOTE: The microphone sensitivity changes with the value of R2 and R3. Usually the

microphones are characterized with 2kΩ biasing resistance, so try to keep the sum of R2 and

R3 around 2kΩ. Refer to your microphone manufacturer for the mic. characteristics.

5.4.2 Unbalanced Microphone biasing

The unbalanced microphone biasing voltage should be obtained from a dedicated voltage regulator, in

order to eliminate the noise present on the power lines. This regulator can be the same for all the

audio paths. The microphone should be supplied from a capacitor multiply circuit.

For example a circuit for the unbalanced microphone biasing can be:

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Telit Wireless Solutions GM862-GPS Manuel d'utilisateur Page 32